Certain types of systems for controlling devices have adjustable settings for control parameters. It is common for these settings to be adjusted by a human operator. A very simple example is the thermostat found in nearly every occupied space. Such settings define either implicitly or explicitly, a control range for the control parameter. The control range is defined by an upper value and a lower value, within which the control system attempts to hold the control parameter by altering a control variable for the device. In the thermostat example, the control variable is usually an on or off signal for the heating plant.
For a variety of reasons, many of these control systems require limits for these control parameter settings. For example, a thermostat might for energy efficiency be designed or programmed to prevent settings outside of a desired temperature range. In other systems, an ultimate maximum (or minimum) value is assigned to a particular parameter for reasons of safety, durability, etc. An example of such a situation (and the one concerning the inventors) involves setting maximum pressure for a boiler.
Every boiler has as one of its critical parameters, a maximum pressure that for safe operation must never be exceeded. Other types of operating systems have other parameters for which an ultimate value must be assigned. In the case of boilers, this maximum allowable pressure will be referred to as the ultimate pressure, and other similar parameter values in other types of systems as ultimate parameter values.
In the case of boiler operation, it is customary to set a maximum operating pressure for the range of allowable pressure levels that is lower than the ultimate pressure. The reasons for this include greater fuel and operating efficiency and increased lifetime for the individual boilers. One system now in use sets the maximum operating pressure and the ultimate pressure for boilers with a maximum pressure potentiometer having a scale for selecting settings. The position of the potentiometer selects the maximum operating pressure, and overrides the control range upper value if set above the maximum operating pressure. A cam or stop on the potentiometer sets the ultimate pressure. When boilers are inspected for safety, the position of the stop on the maximum pressure potentiometer is checked. If higher than the ultimate pressure, the boiler and its operator are in violation, for which a variety of sanctions may be imposed.
There are a number of problems with this system. Potentiometers are electromechanical devices and can fail or drift with respect to the scale over time either with use or with disuse. Tampering with either the ultimate pressure stop or the maximum operating pressure is fairly easy even though access to the potentiometer stop is typically made somewhat difficult.
In electronic control systems, it is cheaper and more reliable for the controller itself to provide the ultimate pressure setting. However, this creates the problem that inspectors (and conscientious operators themselves) cannot easily determine the ultimate pressure setting since most electronic controllers have only rudimentary status indicators. In order to effectively implement ultimate pressure limits in electronic controllers, it is necessary to provide a means for communicating the settings.
We have devised a control system providing a control signal for controlling the activity of an operating system. Our control system sets a system parameter by using a manually adjustable data generation device nominally used to provide a control value signal changing as the data generation device is manually adjusted. The control value signal is often a set point, and in the operating system for which this control system was developed, the set point is a pressure value of a boiler. Controlling the amount of heat energy provided to the boiler by a burner controls boiler pressure. The control signal adjusts the heat output of the burner by regulating the amount of fuel flowing to the burner.
This control system comprises a configuration flag memory element recording a configuration flag having at least first and second values and providing a configuration flag memory signal encoding the configuration flag value. In the embodiment we envision, the configuration flag will be set to its first value at the factory.
A first memory element receives the control value signal and the configuration flag memory signal, and at some point records the control value signal as the system parameter responsive to the first value in the configuration flag memory signal. The first memory element provides a first memory signal encoding the recorded system parameter. For purposes of defining the invention, the first memory element includes not only the data storage components for recording the system parameter, but may also include the control components for processing the signals it receives to effect proper storing of the system parameter.
A second memory element receives the control value signal and records as a set point value, the control value signal. The second memory element provides a second memory signal encoding the recorded set point value.
A control element receives the first and second memory signals, and provides a control signal based on the first and second memory signals and that is usable by the operating system for controlling its operation.
In one version of this invention, the first and second memory signals may be pressure values. The control element uses the first memory signal to set a maximum or safety value for the operating system pressure. The set point value can be changed during normal operation of the operating system by adjusting the data generation device. The maximum pressure value typically varies from system to system, and so cannot be set at the factory. Instead the installer permanently sets the maximum pressure or other system parameter during system installation.
To provide for user communication with the operating system, a reset switch forming a part of the control system provides a reset signal responsive to manual operation thereof. During normal operation the reset switch is used to reset (restart) the system either during testing or after an error or other failure results in the control element locking out normal operation.
During initialization of the system, the first memory element receives the reset signal. The first memory element records the control value signal as the system parameter responsive to the combination of both the first configuration flag value in the configuration flag memory signal and the reset signal from the reset switch.
During an operating system installation procedure, some adjustment and experimentation is typically required to properly set the system parameter. Frequently, the installer will need to watch system operation for a time, and then perhaps change the system parameter. To accommodate such installation procedures, the configuration flag memory element includes a timer element recording a timer value. The control system frequently changes the recorded timer value to indicate elapsed time. The timer memory element provides a timer signal encoding the current timer value. The first memory element receives the timer signal, and records the control value signal as the system parameter responsive to the combination of the timer value falling within a preselected range and an occurrence of the reset signal. The operation of these elements can be used to establish after initializing the system parameter for the first time, a grace period within which the installer can alter (reset) the value of the system parameter.
In a preferred embodiment, the timer element receives the timer signal and sets the timer value recorded in the timer element to a preselected initial value within the preselected range of the timer value responsive to the combination of the timer value falling within a preselected range, and the reset signal. The effect of this combination of functions is to reinitialize the grace period each time the system parameter is reset.
Eventually, the installer will be satisfied with the value selected for the system parameter. After this point, to prevent tampering by unauthorized persons, the control system should prevent further altering of the system parameter. To accomplish this, the configuration flag memory element receives the timer signal, and responsive to the timer value falling outside of the preselected range, sets the configuration flag to the second value. When the second value of the configuration flag is sensed the control system no longer allows the system parameter to be altered.
In a further improvement to this system, the reset switch is designed to provide a separate reset signal responsive to each manual operation. The first memory element receives each reset signal, and records the control value signal as the system parameter responsive to the combination of two sequential reset signals, the timer value falling within a preselected range, and the configuration flag first value in the configuration flag memory signal.
An indicator light providing visible light responsive to a power voltage is another improvement. The indicator light allows for simple communication with the user and installer. A light controller responsive to the timer value falling within a first preselected range, for providing power voltage in a first preselected on-off pattern to the indicator light. This feature assists in alerting an operator that an initial value for the system parameter has not yet been set for the control system. In the preferred embodiment a preset value of the clock signals that an initial value for the system parameter has not yet been set.
A preferred control system""s light controller further provides power voltage in a second preselected on-off pattern to the indicator light responsive to both of i) the configuration flag first value in the configuration flag memory signal and ii) the reset signal. This feature can inform an installer that an attempt to request resetting of the system parameter has been made. This second preselected on-off pattern of the indicator light only means that the reset request was successful. The installer still must select a system parameter value and request that it be accepted.
As previously mentioned, this control system is intended to control a pressure in an operating system such as a water boiler. For such an application the data generation device comprises a manually settable pressure selector. For this case, the control element comprises a level comparator providing the control signal based on the relative magnitudes of the system parameter and the control value. That is, if the pressure set point is set to a value higher than the system parameter value, then the system parameter value is used. This prevents the control system from selecting a set point that is too high.
In one version of the control system for controlling pressure, the system parameter defines the end of a pressure range and the control signal is suitable for controlling the level of a burner flame. The control element comprises a comparator receiving the first and second memory signals, and provides the control signal based on the system parameter when the control value is outside the pressure range, and provides the control signal based on the control value otherwise.